COMPARATIVE STUDY OF THE IMMUNOPATHOLOGICAL RESPONSE IN OCHRATOXIN A, CADMIUM AND MERCURY TOXICITIES IN DUCKS
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Date
1996
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COLLEGE OF VETERINARY AND ANIMAL SCIENCES Mannuthy - Thrissur
Abstract
The present investigation was undertaken for the first time
to assess'the level of contamination of mercury (Hg) and Cadmium
(Cd) in the soil, water, plants and biosamples in localities
where there is significant duck population and to study the
pathological effects of these chemicals and ochratoxin A (OA)
with special reference to immune response in the ducks and duck
embryos. The residues of these chemicals in various tissues of
the ducks were also assessed.
Hg and Cd were detected in all the samples from all the
localities surveyed and its presence especially in the soil,
vegetation, fish, liver and kidney of the ducks from these areas
indicated its public health significance.
After the administration of OA, HgClj and CdClj, there was
dose dependant embryo mortality and reduction in hatchability
rate. The mortality percentage in the highest dose group of
embryos inoculated with HgClj, CdClj and OA was 55s, 51.6s and
48.3% respectively while the hatchability rate was 29.92%, 35%
and 47.83% respectively. This clearly indicated the embryotoxic
action of these chemicals. The body weight, weight of the
thymus, and the bursa of Fabricius was found lowered in the
embryos inoculated with these chemicals. The variations noticed
in the weights at different periods of observation between the
chemicals were also dose dependant. The weight of the spleen of
the embryos inoculated with OA and HgClj was comparable to the
normal embryo but with CdCl^, it was found significantly lowered
in the highest dose group at the 28th day of incubation. These
observations, therefore indicated that Cd has an adverse
significant biological effect on the lymphoid organs of the
developing embryo. Similar effect was observed with Hg and OA
but was relatively low. Histologically, depletion of the
lymphoid elements consequent to degeneration, necrosis and
cytolysis was the characteristic feature in the bursa of
Fabricius and thymus, however, it was comparatively less in the
spleen.
Ultrastructural changes in the lymphoid cells in all these
organs showed membrane alterations, mild to severe mitochondrial
changes, ribosomal detachment and fragmentation of RER and
nucleolar and nuclear changes indicative of cell damage, and
marked reduction in differentiation into plasma cells.
Epithelial cells were also found affected. The toxic effects of
these chemicals were more or less similar in the bursa of
Fabricius, intensity and severity being more with CdClj followed
by HgClj and OA in that order. In the thymus, also, CdCls caused
severe pathological effects while with HgClj intensity was
least. In the spleen there was increased erythrophagocytosis in
addition to these changes and was more severe with HgClj.
In the liver, severe necrobiotic changes were found in the
hepatic cells associated with ultrastructural picture of
organellar damage and lytic changes in the nucleus.
Int6nsity of th6S6 changes was tnore severe in Cd.Cl2 treated
eTubryos followed by those treated with OA and with HgCl2. In
the kidney, the cellular alterations were more in the proximal
convoluted tubules and the intensity of these alterations was
less in OA and CdCl2 treated embryos compared to those treated
with HgClj. The embryos inoculated with OA, HgClj and CdClz,
2-evealed degenerative changes in the lymphoid and other organs.
The adverse immunobiological effects of OA, Hg and Cd on the
developing embryo were established by histological and
ultrastructural studies.
In the ducks, OA, HgCls and CdClj were fed orally (at the
rate of 300 ug, 10 mg and 15 mg/kg body weight respectively) for
90 days. Clinically ducks showed dullness, restlessness and
unusual hyperresponsiveness and inco-ordination of movement, in
OA, HgClj and CdClj fed ducks respectively at the later stage of
the experiment. Progressive reduction in the gain of the body
weight, of the bursa of Fabricius was noticed in all the groups
(OA, HgCl2 and CdCl2 treated) while that of the thymus was
noticed mainly in CdCl2 and OA treated ducks.
There was highly significant reduction in the total
erythrocyte count (TEC), Haemoglobin (Hb) concentration and
Packed Cell Volume (PCV) in the groups fed OA, Hgcl2 and CdCl2.
Highly significant leucopaenia with relative heterophilia and
lymphocytopenia was observed in OA and HgCl2 fed ducks, while
highly significant leucocytosis with heterophilia and
lymphocytopenia was seen with CdClj fed ducks. These
alterations revealed the toxic action of these chemicals on the
haemopoietic cells and the formed elements of the blood.
Estimation of the haemagglutination inhibition (HI)
antibody titre, total serum protein (TSP), serum globulin (SG)
and serum IgG and IgM levels clarified the adverse effect of OA,
Hg and Cd on the humoral immune system, which was evident at an
early stage in Cd and Hg treated ducks while at a later stage in
OA fed ducks. There was marked reduction in the serum IgM and
IgG level in response to New Castle disease Virus (NDV) in ducks
fed HgClj and CdCl^ respectively.
The highly significant reduction in the T-lymphocyte count
in the peripheral blood, increase in the migration indices in
response to NDV in leucocyte migration inhibition test (LMIT),
reduction in cutaneous response to phytohaemagglutinin-M
(PHA-M), 2,4-dinitrochlorobenzene (DNCB) and the decreased
spleen indices in Graft versus host reaction (GVHR) indicated
the toxicity of OA and Cd on the cell-mediated immunity, which
was more pronounced and evident at an early stage in Cd treated
ducks than compared to OA treated ducks. However, the results
of the migration indices, PHA-M cutaneous response and GVHR
demonstrated that the CMI response escape the toxic insult of
the Hg and is dependant on the duration of exposure, which was
clarified by T-cell dependant lymphocytopaenia and reduction in
cutaneous response to DNCB at the last week of the experiment.
Significant reduction in the phagocytic ability in all the ducks
treated either with OA, HgClj or CdClj was observed by carbon
clearance assay.
There was reduction in the weight of the bursa of Fabricius
and spleen. The thymus showed focal areas of congestion and
petechiae in Cd induced toxicity, and was found appreciably
reduced and atrophied with Cd and at the later stages with OA.
Degenerative and retrograde changes indicative of necrobiosis
were observed histologically. Ultrastructural changes were more
severe with CdClj followed by HgCl2 and OA in that order. In the
spleen of ducks fed CdClj there were proliferative changes
initially followed by degenerative changes at later stages. In
the thymus, effect of the Cd was more severe on the lymphocytes
followed by OA and was least with HgCla.
Histological and ultrastructural studies revealed
degenerative nephropathic changes in the kidney associated with
Hg, OA and Cd toxicity. Intensity of alterations was more with
Cd.
The hepatic lesions characterised by moderate to severe
hepatosis were more pronounced in the case of Hg and Cd in an
increasing order. Histological and electron microscopic studies
elucidated the neuropathological changes associated with Hg, Cd
and OA toxicity.
Estimation of OA, Hg and Cd residues indicated a steady
increase in the accumulation of these substances in the various
tissues depending on the dose and duration of exposure. Highest
concentration of OA, Hg and Cd was detected in the kidney,
followed by liver. Residues of these substances at varying
concentrations were also detected in the muscles, brain, spleen,
bursa of Fabricius and thymus.
This study brought to light the immunosuppressive effect of
OA, Hg and Cd which would compromise the dichotomous defence
mechanism of the ducks. Also adverse effects on hepatic,
haemopoietic, renal and nervous system were documented. It was
clarified by this investigation that immunotoxic effect of these
chemicals could lead to breakdown of immunity and outbreak of
diseases when the ducks are maintained in a polluted
environment. The need for the systematic monitoring of the
environment and taking appropriate steps to prevent
environmental pollution were stressed. The public health
importance of residues of these chemicals was brought to light.
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